Resistance unit



Dec. 27, 1932. F. H. BULLINGER 1,892,202

RESISTANCE UNIT Filed July 14. 1930 -Patentcd D... 27, 1932 UNITED STATES,

PATENT OFFICE FREUEBIC H. BULLINGER, OF BBONXVILLE, NEW YORK, ASSIGNOR '1'0 WARD LEONARD ELECTRIC OOMPANY, A CORPORATION OF YORK nnsrsrimcn um'r Application filed July 14,

' i This invention relates to resistance units,

' the terminal leads to the tube and for connection of the resistive conductor to the leads such that there will be no objectionable bump or projection on the tube which cannot be readily covered by the insulating coating.

Another object is to avoid a twist in the lead wires where they leave the tube, because such a twist causes a weakening at such points where it is most desirable that the leads should have their full strength vand freedom of flexibility withoutbeing subjected toadditional and unnecessary strains at such points. The lead wire is'ordinarily stranded or braided to permit convenient connection of the unit into the desired circuit and to avoid breaking, but continued use causes repeated flexing of the lead wires at the points where they leave the insulating coatin v on the tube. Thus, the avoidance of any initial strains at such locations will obviously prolong the use of the unit. It has been common to use stranded lead wires which tightly encircle the tube and are twisted together to I form their own support upon the tube and to which the resistive conductor is connected. But in firing or baking for maturing the insulating 1930. Serial No. 467,674.

ductor. Thus, another object of the present invention is to provide a'support and connection.of the lead wire such that undesirable looseness or shifting cannot take place.

I accomplish this by use of an auxiliary support for the terminal copper lead which support envelops the tube and also serves to support the copper lead. The auxiliary support is made of a metal having a lower coefficient of expansion than copper, such as iron or steel. Also, by reason of such metal having a higher tensile strength than that of'the copper lead wire, it may be made of comparatively small size and yet be amply strong, while at the same time presenting a smaller surface to be covered by the insulating coating, and likewise avoiding undesirable protruding bumps or projections. Another advantage of this invention is that by the use of iron or steel, or similar metal, for the terminal support, the expense is reduced, owing to its lower cost compared to the use of a copper stranded conductor encircling) the tube to form the terminal connection. ther objects and advantages of this invention will be understood from the following description and accompanying drawing.

Fig 1 is a longitudinal section of oneembodiment of this invention; Fig. 2 is aside view showing theparts before the application of the insulating coating; and Fig. 3 is a similar view of a modified form.

The insulating tube 1 is preferably of porcelain. The resistive conductor'2 is wound around the tube in successive spaced turns and I erable,owing toitshightensile strength and its coeflicient of expansion being lower than that of copper. Before the iron wire is mounted on the insulating support, it is wound around or twisted around the copper lead. lwire V by a few turns, the lead wire 4 being preferably of copper and stranded or braided. Fig.

4a lying against the body of the tube; and also an outwardly extending end for forming the terminal lead. The wire 3 isfirmly secured around the tube by twisting the two ends of the wire together as indicated at 3a. This clamping of the wire around the tube also serves to give the lead wire a firm support on the tube, and it is evident that where the lead wire leaves the tube, there is no twisting strain or tension upon it. One of the ends of the resistive conductor 2 is wound several times around the end 4a of the lead wire and then continues in successive turns around the .tube where it is similarly wound around the projecting end 4a of the lead wire at the other end of the tube. The resistive conductor, where it is wound or twisted around the end 4a of the lead, is preferably soldered, brazed, or otherwise intimately connected therewith. The tube is then covered by the insulating material and dried, baked or fired to form the insulating protective coating 5, which is preferably adhesive vitreous enamel. While soft solder may be used to unitethe ends of the resistive conductor with the ends 4a of the leads, where the conductor is twisted or wound around these ends, it is preferably, when a vitreous enamel coating is used, to braze, or silver-solder, with a material that is higher in melting point than the temperature at which the enamel is matured, although this is not essential. The right-hand terminal,

2, indicates the soldering of the end 4a F arid of the resistive conductor, while the lefthand terminal of Fig. 2 shows the resistive conductor wound around the end 4a before soldering.

The structure shown in, Fig. 3 is similar to that already described, except'that the twisting of the ends of the iron wire 3 is made at the location of the projecting end 4a of the bracin and conveniently assembled with low cost of labor. The structure evidentl obtains the objects already referred to an is advanta geous over prior construction in many respects.

Although I have disclosed preferred embodiments of my invention it is apparent that modifications may be made therein without departing from the scope thereof.

I claim:

A resistance device comprising a support, a resistive conductor thereon, a metal wire emsaid support and having its ends twis together, a conductive wire terminal held in position on said su port by said element, said metal wire an conductive wire being wound one around the other said resistive conductor being directl mechanically and electrically connected wi "said conductive wire, said metal wire bein of a metal having a higher tensile st and lower coeficient of expansion than the metal of said conductive wire, and an insulating coa covering said resistive conductor and terminal connection.

FREDERIC H. 'BULLINGER.

lead wire; and the two ends of the iron wire Y and the end 4a are all three twisted together as indicated at 6 in Fig. 3. The resistive eonductor isthen wound several times around the twisted ends, after which the parts are soldered as indicated at 6a to insure a good electrical connection between the resistive conductor and the terminal lead wire 4.

' Itisapparent thatbythe use of my improve- I ment, the sine'oflthe iron wire 3 may be made comparatively small. I The form of anchoringeofthe lead wire to the wire 3 and to the to is accomplished'without forming any objectionable portion protruding from the tube, and likewise the twisted ends of the iron wire form'only a small protuberance, even when the end of the terminal lead is twisted-with them, thus permitting the insulating coating to thoroughly cover the (parts and securely bind them to the tube an likewise avoiding undue pro'ections which might be subject to hitting or reaking in future hand The structure is also economical in cost o austerial, and by reason of its simplicity, is readily 

